1. Field of the Invention
The present invention is directed to an apparatus for the anaerobic treatment of urban or industrial waste water, and particularly diluted effluents as well as effluents exhibiting a high degree of pollution and, preferably, effluents which are difficult to degrade.
The invention is specifically directed to anaerobic treatments wherein a degradation of the fermentation organic pollution is caused in a closed reaction vessel, called fermentor, in presence of methanogene bacteria, the slurries formed being left to decant in order to be recycled in the fermentor so as to provide therein a high concentration of purifying microorganisms. The slurries in excess are regularly extracted from the apparatus.
In order to practice such a treatment, it is important to design an apparatus in which the recycling of the slurries from the decantation vessel to the fermentor is carried out in a simple manner, and in which a sufficient separation of the slurries can be carried out despite the presence of the gas formed during the fermentation in the reaction vessel.
2. Discussion of Background and Material Information
The standard apparatus conventionally used for such purpose include a fermentor and a separated clarifying tank, the slurries being recycled from the clarifying tank to the fermentor by pumping. In order that the slurries can build up so as to be drawn-off, it is necessary that the clarifying tank be very deep, steeply inclined, and therefore bulky. Alternatively, the tank can be scraped by means of an immersed mechanical equipment which tends to cause corrosion. Moreover, such apparatus have the disadvantage of being difficult to cover up and therefore of causing odor problems. In addition, the heat losses due to the transfer of the slurries can be high and necessitate a re-warming of the slurries prior to their recycling to the fermentor. Notwithstanding, the stability and rapidity of the anaerobic digestion is better if the temperature of the slurries remains constant.
Apparatus in which the clarifying tank is integrated to the fermentor have already been described. If they mitigate some of the hereabove disadvantages, i.e., they are less bulky, do not risk emitting smells and eliminate the risk of thermal shock to the slurries, they are nevertheless complex in their construction and difficult to use when diluted effluents are involved with structures that cannot be sufficiently large. Moreover they necessitate the presence of gas separators integrated in the apparatus between the fermentation zone and the decantation zone, and they do not solve the degassing problem in the decantation vessel as such where the methanization is taking place.